The following patents are noted as being relevant to the field of the present invention:    U.S. Pat. No. 7,509,880 “Fluid flow meter body with high immunity to inlet/outlet flow disturbances” to Kurz;    U.S. Pat. No. 7,299,707 “Eccentric venturi flow meter” to Evans;    U.S. Pat. No. 7,281,436 “Wedge flow meter with conditioner” to Orleskie;    U.S. Pat. No. 7,096,738 “Inline annular seal-based pressure device” to Schumacher;    U.S. Pat. No. 6,799,477 “Flow metering device for landfill gas extraction well” to Brookshire;    U.S. Pat. No. 6,725,731 “Bi-directional differential pressure flow sensor” to Wiklund;    U.S. Pat. No. 6,672,173 “Flow meter” to Bell; U.S. Pat. No. 5,616,841 “Flow metering device for landfill gas extraction well” to Brookshire;    U.S. Pat. No. 4,926,698 “Dual wedge flow element” to Owen;    U.S. Pat. No. 4,237,739 “Integral flow metering assembly using a segmental wedge” to Owen;    U.S. Pat. No. 4,102,186 “Method and system for measuring flow rate” to Brown; and    GB Patent No. 2217462 to Brady.
Global surface temperature warming is believed by the Intergovernmental Panel on Climate Change, among others, to be caused by increased concentrations of green house gases resulting from human activities. Man-made global warming, as it is commonly called, is perceived as a serious threat by scientists and legislative bodies in the United States of America (USA) and across the globe. Laws and international treaties addressing this threat have been, and will be, discussed, negotiated and passed. In the USA prospective legislation on “Cap and Trade” is advocated by President Obama, House Speaker Pelosi and Senate Majority Leader Reid related restrictive legislation in the USA appears inevitable. Regardless of the legitimacy of the science or the status of such legislation or treaties there are legitimate reasons to control and reduce green house emissions. It is axiomatic measuring and monitoring these gases, in particular the emissions thereof, invariably will play a critical role in their control and reduction.
Landfills are often prolific contributors of green house gases, particularly methane (CH4) which according to the EPA is a greenhouse gas approximately 21 times more potent than carbon dioxide (C02), emissions. A common method of waste disposal and treatment, landfills produce these gases, among others, from the anaerobic digestion by microbes of organic matter. These gases, typically composed of mostly methane and carbon dioxide, may be collected and methane in particular may be utilized, with contemporary technology, to generate electricity by combustion, fuel industrial boilers, or be converted to pipeline quality High-BTU gas. In utilizing the methane from the landfill, greenhouse gas emissions are greatly reduced.
Landfills frequently have gas extraction systems to capture landfill gases. Gases are typically drawn out of a landfill with a low pressure vacuum via a wellfield collection system. The wellfield typically consists of multiple gas extraction wells that extend deep beneath the surface of the landfill to pull methane from a location near the bottom of the landfill. Each extraction well extends up to the surface of the landfill and there the extraction wells are manifolded together so that vacuum can be pulled with one centralized blower or compressor.
It is critical to regulate the vacuum draw on the landfill well field. In order to do so, each extraction well must be continuously monitored for flow and gas quality. Measuring the gas flow at the head of each extraction well permits an operator with a gas analyzer to compile the total gas quality and volume produced by a landfill well field and may assist in making decisions based thereon. Regulating the vacuum or draw on the field regulates, to a degree, the type and rate of decomposition. Too much draw may pull oxygen into the well field enabling aerobic decomposition and causing underground fires thus requiring shutdown of the well field resulting in unrestricted release of greenhouse gases into the atmosphere. Too small of a draw will increase gas diffusion into surrounding soil and eventual release of methane into the atmosphere. Typically each extraction well utilizes a valve at the head of the well to adjust the vacuum pulled on the well. After monitoring the extraction well's gas flow and composition, an operator may adjust this valve to optimize gas recovery or limit oxygen pull into the landfill.
Landfill gas monitoring and recovery could be referred to as a wet gas industry because the gases created in landfills produce water in addition to oxygen, nitrogen, methane and carbon dioxide. Typically landfill gas is collected from the well field 100 percent saturated or as a wet gas. The wet gas, the possibility of particulates, and low pressures associated with these systems present some significant challenges for gas measuring devices. The prior art is replete with devices used to calculate gas flow. The Venturi effect is well known in the art wherein constricted fluid flow results in differential pressures from which flow can be calculated. Fluid flow may be measured with an orifice plate or a Pitot tube, both of which are well known in the art and are considered the industry standards for landfills today. Other wedges and eccentric devices which recognize the Venturi Effect and Bernoulli's principles may be used to create differential pressure in a pipe in order to measure gas flow. The orifice plate design utilizes an abrupt restriction in the flow to create a differential pressure for calculating flow. Because of the abrupt restriction there is a high loss in applied vacuum to the extraction well being monitored. Given the low pressures involved and the desire to regulate the extraction well's vacuum it is preferred that the measuring device has a minimal impact on system pressure. Additionally, the abrupt restriction of a concentric or eccentric orifice plate does not allow the unobstructed pass-through of liquids and possibly particulates. The retaining of liquids at the orifice plate impacts the flow measurement and the liquid is often ingested into the pressure monitoring equipment, or flow monitoring equipment, which is extremely detrimental to the internal sensors. Over time, if too much water builds up at the orifice plate, the orifice can become plugged entirely, cutting off vacuum to the extraction well and resulting in unrestricted release of methane into the atmosphere. Pitot tubes work on the principle of calculating flow through the process of determining the velocity of ram pressure as compared to the static pressure. Because landfill gas is typically both a wet and dirty gas, with particulates (solids) a Pitot tube monitoring device is often plugged at the ram air pitot port. Despite these drawbacks and limitations, including their propensity for erroneous pressure readings due to clogging of orifices and pitot ports, orifice plates and pitot tubes are currently considered the landfill gas industry standards for measuring extraction well flow.
The prior art includes U.S. Pat. No. 1,706,145 “Differential Pressure Device.” FIG. 1 in said patent depicts an eccentric Venturi device for purposes similar to the subject invention and of a design similar to the subject invention.